1. Field of the Invention
The present invention relates to a multi-stage lens driving device and, more particularly, to an optical lens driving device operated on electromagnetic fields for multi-stage focusing and/or zooming.
2. Description of the Prior Art
Refer to FIG. 1, which shows a mechanical-transmission focusing device 90 as used in a conventional photographing apparatus. The focusing device 90 uses a high-cost precision driving element 91 (e.g., a step motor, ultra-sound motor, piezoelectric actuator, etc.) as a power source for driving a seat 93 holding a lens set 92, and includes a large number of transmission elements. Such design not only results in a complicated mechanical configuration, but also requires a complex assembly process with numerous steps, leads to a bulky size and high cost, and poses such serious problems as high power consumption.
Photography in the old days was an elaborate technique depending on manual light measuring, focusing by hand, and self-assisted film winding. However, where heavy manual operation is required, errors tend to ensue. Therefore, in this period of time, the qualification of a photographer was essential, especially on important shooting occasions that would not take place again. With the substantial development of machine automation in the 1950s and 1960s, more and more people had come to believe that automation would be a guide to the future world. Then the development of the automatic light-metering techniques and power film winders have sufficiently revealed the prospects of the photography towards automation; and an “automatic focusing system”, which is the most critical part in photography automation and an important factor dominating the shooting speed, has become a highlighted item for many camera manufactures to research and develop.
With rapid advancement of technology, traditional professional photographing apparatuses not only have improved in terms of image quality, but also are made lighter, thinner and smaller to be lined with the modem products of this diversified information era. Therefore, a focusing and/or zooming lens mechanically driven by a step motor has become disadvantageous because its size cannot be further reduced, thereby preventing the final assembled products from being smaller and lighter. On the other hand, manufactures have turned to electromagnetic technologies and used VCM electronic feedback systems to monitor the deviation of coils in order to replace conventional step motors and further downsize the driving structures. Meanwhile, there is a trendy to integrate products with various functions. For example, the photographing function may be integrated into mobile phones, personal digital assistants (PDAs) or notebook computers, so as to provide more powerful video functions. Therefore, regarding to manufactures' designing a product having different functions that share a single power supply, it is a major research and development issue to reduce the size, the cost and power consumption, so that the product is endowed with increased standby time and operation time while using power supplies of the same capacity.